Compression force sensor for a handheld electromechanical surgical system

ABSTRACT

A surgical device includes a tool assembly and a handle assembly. The tool assembly includes a distal portion including a plurality of staples and an anvil assembly movable relative to the distal portion from an open position to a clamped position. The handle assembly includes an approximation mechanism coupled to the anvil assembly and configured to move the anvil assembly from the open position to the clamped position, a force sensor disposed at a distal end of the surgical device, and a controller. The force sensor is configured to sense a change in resistance indicating a force imparted on compressed tissue and on the approximation mechanism. The controller is configured to receive a signal indicative of a force measured by the force sensor and provide an indication of the sensed force.

BACKGROUND Technical Field

The present disclosure relates to surgical devices. More specifically,the present disclosure relates to handheld electromechanical surgicalsystems for performing surgical procedures having a force sensorconfigured to monitor compression forces during tissue clamping,stapling, and/or cutting.

Background of Related Art

Circular stapling devices are used to perform a variety of proceduresinvolving anastomoses in which two tubular anatomical tissue structuresare joined together. These procedures include colorectal circularanastomoses, esophageal circular anastomoses, and bariatric circularanastomoses. Typically, a circular stapling device includes a toolassembly and a handle assembly. The tool assembly includes an anvilassembly and a reload that are movable in relation to each other inresponse to actuation of an approximation mechanism that clamps tissuebetween the anvil and reload assemblies. The reload includes a staplecartridge, a staple pusher, and an annular knife. The staple cartridgesupports one or more annular rows of staples, and the staple pusher ismovable within the staple cartridge in response to actuation of a firingmechanism to eject the staples from the staple cartridge into the anvilassembly. The annular knife is positioned radially inward of the annularrows of staples and is movable from a retracted position to an advancedposition to cut or core tissue against a cut ring of the anvil assembly.

The circular stapler may be used during an end-to-end anastomosisprocedure, during which two portions of a structure (e.g., intestine,colon, etc.) are reconnected, after the diseased tissue is removed. Oneend of the structure is attached to the anvil, and the opposite end isattached to the staple housing, or cartridge. The two ends of thestructure are brought together before creating the anastomosis. Somecircular staplers may have a visual gauge that indicates the tissue gapbetween the anvil and cartridge of the stapler, which displays thedistance traveled by the anvil. As the surgeon operates the rotary inputmechanism to approximate the anvil to the cartridge, the visual gaugemoves into a region that shows it is “safe” to fire the stapler andcreate the anastomosis. This visual gauge ensures that the stapler isonly fired once an appropriate gap has been set. The rotating clampmechanism also provides beneficial haptic feedback while surgeons arecompressing both ends of tissue together. However, both the visualfeedback from the gauge and the haptic feedback are subjective andsuboptimal. The gauge only factors in distance traveled rather thanpressure, and the haptic feedback from the clamping mechanism varies dueto broad ranges of surgeon strength and experience. The current systemmakes it difficult for other surgeons to train because clamping methodsare subjective. This leads to circular stapler usage inconsistencies. Acontinuing need exists for a circular stapling device that has theadvantages of monitoring pressure during surgery, avoiding tissue damagedue to a fast rate of compression or over compression, and providingfeedback to the surgeon.

SUMMARY

This disclosure generally relates to a surgical stapling device forperforming procedures involving anastomoses within a body of a patient.The surgical stapling device includes a handle assembly that includes amanually actuated approximation mechanism and a motorized firingmechanism.

In accordance with aspects of the disclosure, a surgical device includesa tool assembly and a handle assembly. The tool assembly includes adistal portion including a plurality of staples and an anvil assemblymovable relative to the distal portion from an open position to aclamped position. The handle assembly includes an approximationmechanism coupled to the anvil assembly and configured to move the anvilassembly from the open position to the clamped position, a force sensordisposed at a distal end of the surgical device and configured to sensea change in electrical resistance indicating a compression forceimparted on tissue, and a controller configured to receive a signalindicative of a force measured by the force sensor and provide anindication of the sensed force.

In an aspect of the present disclosure, the indication of the force mayinclude visual feedback, haptic feedback, and/or audible feedback basedon the measured force.

In another aspect of the present disclosure, the force sensor mayinclude a force sensitive resistor.

In yet another aspect of the present disclosure, the force sensitiveresistor may include a substrate including a proximal side and a distalside, a conductive trace deposed on the distal side of the substrate,and a conductive material deposed on the conductive trace.

In a further aspect of the present disclosure, the trace may include aninterdigitated pattern.

In yet a further aspect of the present disclosure, the conductivematerial may include a conductive sheet or a conductive ink.

In an aspect of the present disclosure, the conductive material mayinclude conductive and non-conductive particles suspended in a matrix.

In another aspect of the present disclosure, the controller may befurther configured to transmit the indication of the sensed force to adisplay.

In yet another aspect of the present disclosure, the controller may befurther configured to determine if the sensed force is within a forcerange and provide an indication that clamping forces on the tissue aresafe.

In a further aspect of the present disclosure, the distal portion andthe anvil assembly may be circular.

In accordance with aspects of the disclosure, a method for providing anindication of force for a surgical device, includes sensing a forcemeasured by a force sensor disposed in the handle assembly of a surgicaldevice. The distal force sensor is configured to sense a change inresistance indicating force between the anvil and cartridge, andinforming usage of the approximation mechanism of the surgical device.The method further includes providing an indication of the sensed forceduring clamping of tissue.

In an aspect of the present disclosure, the method may further includetransmitting the indication of the sensed force to a display.

In another aspect of the present disclosure, the method further mayinclude determining if the sensed force is within a force range andproviding an indication that it is safe to fire the surgical device.

In yet another aspect of the present disclosure, the indication of theforce may include at least one of visual feedback based on the sensedforce, haptic feedback, and/or audible feedback based on the sensedforce.

In a further aspect of the present disclosure, the force sensor includesa force sensitive resistor.

In accordance with aspects of the disclosure, a force sensor configuredto sense a change in resistance indicating a force imparted on anapproximation mechanism is presented. The force sensor includes asubstantially circular substrate including a proximal side and a distalside, a conductive trace deposed on the distal side of the substrate,and a conductive material deposed on the conductive trace.

In another aspect of the present disclosure, the trace may include aninterdigitated pattern.

In yet another aspect of the present disclosure, the conductive materialmay include a conductive sheet or a conductive ink.

In a further aspect of the present disclosure, the conductive materialmay include conductive and non-conductive particles suspended in amatrix.

In yet a further aspect of the present disclosure, the conductivematerial may include a distal side and a proximal side. The force sensorfurther includes an actuator disk disposed on the distal side of theconductive material.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects and features of the disclosure are described withreference to the drawings wherein like numerals designate identical orcorresponding elements in each of the several views wherein:

FIG. 1 is a perspective view of a handheld surgical device including ahandle assembly, an elongate body, and a tool assembly, according to anembodiment of the present disclosure;

FIG. 2 is a schematic diagram of the handle assembly, the elongate body,and the tool assembly of FIG. 1 ;

FIG. 3 is a side, cutaway perspective view of the handle assemblyincluding a force sensor, according to an embodiment of the presentdisclosure;

FIG. 4 is an exploded view of a force sensor of FIG. 3 ;

FIG. 5 is a top view of a printed circuit board of the force sensor ofFIG. 3 ;

FIG. 6 is a side, cutaway view of the handle assembly of FIG. 1 ;

FIG. 7 is a perspective view of the handle assembly of FIG. 1 ,including a visual indicator, according to an embodiment of the presentdisclosure; and

FIG. 8 is a method for controlling the surgical device of FIG. 1 duringthe stapling sequence according to an embodiment of the presentdisclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the presently disclosed surgical devices are described indetail with reference to the drawings, in which like reference numeralsdesignate identical or corresponding elements in each of the severalviews. As used herein the term “distal” refers to that portion of thesurgical device, or component thereof, farther from the user, while theterm “proximal” refers to that portion of the surgical device, orcomponent thereof, closer to the user.

The present disclosure provides a powered circular stapler having ahandle assembly, an elongate body coupled to the handle assembly, and atool assembly coupled to the elongate body. The tool assembly includesan anvil assembly and a cartridge assembly.

The disclosed technology provides feedback to users regarding thepressure that is being applied between the anvil assembly and thecartridge assembly by integrating a force sensor into the circularstapling device to monitor pressure during clamping and providing visualfeedback to the user. The disclosed technology ensures users of thestapler do not impose excessive amounts of pressure on the tissue duringthe clamping phase across all tissue types and tissue thicknesses. Thisensures intended device performance during clamp, giving the best resultfor the patient and the user.

The goal of the feedback is to reduce and/or eliminate the subjectivityof the applied clamp force by providing a consistent indicator of clampforces across all EEA stapling surgeries. This indicator will providethe surgeon or resident the information needed to prevent exceedingoptimal compression forces on tissue during the clamping phase as wellas aid in accounting for fluids diffusing out of the staple region toreduce stress on tissue and vasculature.

FIG. 1 illustrates a surgical device 1, such as, for example, a poweredcircular stapler for forming end-to-end anastomosis (“EEA”), including ahandle assembly 100. The surgical device 1 which includes a handleassembly 100, an elongate body 200, and a tool assembly 700. The toolassembly 700 includes an anvil assembly 500 that has an annular stapleforming surface (not shown) and a distal portion 400 that has an annularstaple cartridge (not shown) that supports staples (not shown). Theanvil assembly 500 is supported for movement in relation to the distalportion 400 between an open or unclamped position (FIG. 1 ) and aclamped position. In aspects of the disclosure, the distal portion 400includes a proximal portion that is coupled to a distal portion of theelongate body 200 includes a proximal portion that is coupled to thehandle assembly 100. It is envisioned that the distal portion 400 can bereleasably secured to the elongate body 200 and/or the elongate body 200can be releasably secured to the handle assembly 100. The distal portionalso includes a knife (not shown) that is movable between retracted andadvanced positions to cut tissue during an anastomosis procedure.

The surgical device 1 includes a hybrid type handle assembly 100 thatincludes a manually operated approximation knob 101 for approximatingthe anvil assembly 500 with the distal portion 400 and a fire button 20for activating a motor 152 for stapling and cutting tissue. The handleassembly 100 includes a body portion 10 b that is ergonomically shapedto be gripped by a clinician. The body portion 10 b defines an internalcavity (not shown) and an external recess (not shown). The internalcavity receives drive components of the handle assembly described below.The external recess receives a battery pack that is releasably coupledto the body portion 10 b of the handle assembly 100. The approximationknob 101 opens/closes tool assembly 700 (when anvil assembly 500 isconnected to the trocar member).

The handle assembly 100 includes a fire button 20 that can be pressed toclose a fire switch (not shown) and initiate firing of the surgicaldevice 1, e.g., activate the motor 152 to advance a pusher link andadvance the pusher (not shown) to fire staples from the distal portion400. The fire button 20 may also be illuminated such as a with a lightemitting diode (LED). For example, if a safety button (not shown) ispressed, and other necessary conditions are met, the pressing of thesafety button (not shown) will arm the surgical device 1, and the firebutton 20 will illuminate to provide an indication to a clinician thatthe surgical device 1 is ready to be fired.

In aspects of the disclosure, the fire button 20 may be configured toblink when the surgical device 1 is coupled to the battery 144 prior tomovement of the surgical device 1 to the clamped position.

With reference to FIG. 2 , the handle assembly 100 includes a controllercircuit board 142, a battery 144 configured to supply power to any ofthe electrical components of handle assembly 100, and a motor 152coupled to the battery 144. The handle assembly 100 also includes adisplay 202 (such as LEDs, and/or an OLED display). The controller 147is coupled to the force sensor 300 of the handle assembly 100 using awired or a wireless connection and is configured to receive forcemeasurements from the force sensor 300 which are used during operationof the handle assembly 100 to indicate the clamping force on tissue. Thecontroller may further be coupled to the visual indicator 202 to providea visual indication of the force measurements.

In embodiments, the motor 152 may be coupled to any suitable powersource configured to provide electrical energy to the motor 152, such asan AC/DC transformer or a battery. The motor 152 is coupled to a motorcontroller 143 which controls the operation of the corresponding motor152, including the flow of electrical energy from the battery 144 to themotor 152. A controller 147 is provided that controls the handleassembly 100. The controller 147 is configured to execute softwareinstructions embodying algorithms disclosed herein, such as clamping,stapling, and cutting algorithms which control operation of the handleassembly 100.

The controller 147 is also coupled to a memory 141. The memory 141 mayinclude volatile (e.g., RAM) and non-volatile storage configured tostore data, including software instructions for operating the handleassembly 100.

The handle assembly 100 includes a plurality of motors 152 eachincluding a respective motor shaft (not explicitly shown) extendingtherefrom and configured to drive a respective transmission assembly.Rotation of the motor shafts by the respective motors function to driveshafts and/or gear components in order to perform the various operationsof handle assembly 100, for example cut tissue, or fire staples. Inparticular, motors 152 of handle assembly 100 are configured to driveshafts and/or gear components in order to selectively extend/retract afiring mechanism (not shown), fire an annular array of staples of distalportion 400, and move an annular knife (not explicitly shown) of distalportion 400.

Turning now to FIG. 3 , the handle assembly 100 including a force sensor300 is shown. The force sensor 300 may be disposed within a distalportion of the handle assembly 100, proximal to outer tube 206. Theforce sensor 300 is configured to sense force when the outer tube 206 isforced in a proximal direction where the force sensor 300 can sense aforce. For example, force may be sensed by the force sensor 300 whenclamping, stapling, and/or cutting tissue grasped within the toolassembly 700 (FIG. 1 ). During clamping, stapling and/or cutting, areaction force is exerted on anvil assembly 500 and the distal portion400, which then communicates the reaction force to a force sensitiveresistor of the force sensor 300.

Referring to FIGS. 4 and 5 , the force sensor 300 of the surgical device1 is shown. The force sensor 300 may be a force sensitive resistor(FSR), also known as a force sensing resistor. A force sensitiveresistor is an electrical device whose resistance changes when a force,pressure or mechanical stress is applied. The force sensor 300 functionsas a variable resistor whose resistance decreases when the applied forceincreases. Force may be determined by the controller 147 based on thechange in resistance.

The force sensor 300 includes a printed circuit board 310 and aconductive material 320. The printed circuit board 310 generallyincludes a substrate 312 and a conductive trace 314 (e.g., gold platedcopper trace(s)) deposed on the distal side of the substrate 312 Thesubstrate 312 may be made from a suitably flexible material (e.g., amembrane). The conductive trace 314 may include an interdigitatedpattern configured to change resistance when pressure is applied to theconductive material 320. The conductive trace 314 includes a firstterminal and a second terminal configured for electrical communicationwith the controller 147. Although shown as a disk, it is contemplatedthat the force sensor 300 may be any suitable shape (e.g., square, oval,elliptical, etc.).

The conductive material 320 may be a conductive sheet and/or aconductive ink. The conductive material 320 may include conductive andnon-conductive particles suspended in a matrix. In aspects, a spacer(not shown) may be disposed between the conductive material 320 and theconductive trace 314.

The conductive material 320 (e.g., a conductive polymer) includes aproximal side 324 disposed on the distal side 318 (on the conductivetrace 314) of the printed circuit board 310, and a proximal side 322configured to engage an actuator disk 330. The actuator disk 330 may bemade of a suitably rigid material, such as steel, however, othermaterials are contemplated.

With reference to FIG. 6 , an alternate proximal location for the forcesensor 300 for sensing force when clamping tissue. The proximal forcesensor 301 is substantially similar to the more distal force sensor 300.The handle assembly 100 includes a manually operated approximation knob101 for approximating the anvil assembly 500 with the distal portion 400and a fire button 20 for activating a motor 152 (FIG. 3 ) for staplingand cutting tissue. Rotating the approximation knob 101 causeslongitudinal movement of the anvil assembly 500 with respect to thedistal portion 400.

The handle assembly 100 includes approximation mechanism 714 whichincludes the approximation knob 101, an anvil clamp screw (not shown), arotatable sleeve 716, a screw resilient extension (not shown), and ananvil retainer trocar (not shown). The rotatable sleeve 716 includes acylindrical hollow body portion (not shown) and a cylindrical collar 718supported on a distal portion of the hollow body portion. The rotatablesleeve 716 defines a longitudinal through bore (not shown). The collar718 has a diameter greater than the body portion 10 b and is receivedbetween inwardly extending flanges 92 formed on inner walls of the bodyportion 10 b of the handle assembly 100. Receipt of collar 718 betweenthe flanges 92 axially fixes the rotatable sleeve 716 within the bodyportion 10 b of the handle assembly 100 while permitting rotation ofrotatable sleeve 716. It is contemplated that the approximationmechanism 714 may be manually operated or powered.

A proximal portion of the rotatable sleeve 716 extends through anopening (not shown) in the proximal end of the body portion 10 b of thehandle assembly 100 and is fixedly coupled to the approximation knob101. The hollow body portion of the rotatable sleeve 716 includes a pairof diametrically opposed ribs (not shown) that are formed on the outersurface of the body portion (not shown) and are received within slots(not shown) defined within the approximation knob 101 to rotatably fixthe rotatable sleeve 716 to the approximation knob 101 such thatrotation of the approximation knob 101 causes concurrent rotation ofrotatable sleeve 716.

Rotation of the approximation knob 101 moves the anvil assembly 500 inrelation to the distal portion 400 between the open and clampedpositions. U.S. Pat. No. 7,303,106 describes a stapling device includingan anvil assembly 500 and anvil retainer that are releasably coupledtogether and are suitable for use with the surgical device 1.

The force sensor 300 may be disposed within the handle assembly 100,proximal to the cylindrical collar 708. The force sensor 300 isconfigured to sense force when the cylindrical collar 708 is forced in aproximal direction where the force sensor 300 can sense a force. Forexample, force may be sensed by the force sensor 300 when clampingtissue grasped within the tool assembly 700 (FIG. 1 ). It iscontemplated that a force sensor 300 may be used to sense force whenstapling and cutting issue.

For further details regarding the construction and operation of thecircular stapler and its components, reference may be made to U.S.Application No. 63/140,066, filed on Jan. 21, 2021, the entire contentsof which being incorporated by reference herein.

FIG. 7 shows a perspective view of the handle assembly 100 of FIG. 1 ,including a visual indicator 202 (e.g., visual feedback). The handleassembly 100 may include visual indicators 202 for providing visualfeedback to the user to indicate how much force the user is applyingduring tissue clamping. This indication may complement haptic feedbackprovided by the manually controlled approximation knob 101. In aspects,the visual indicator 202 may include one or more LEDs 702, 704, 706(e.g., a green and red light, a green/yellow/red light system, and/or amulti-color light), an OLED display, an LED display, and/or a series offlashing lights. An additional benefit of implementing visual feedbackis that the lights and/or screen can be visible to both surgeons andresidents, thereby creating potential to be a training tool forstreamlined EEA clamping.

The visual feedback may include a series of lights (colors or flashingpatterns) where it will be clear whether the surgeon is in a low forceor high force range of applied force.

With reference to FIG. 8 , which shows a method for providing anindication of force for a surgical device, during clamping, as theapproximation knob 101 advances the anvil assembly 500, the controller147 continually monitors the force measured by the force sensor 300.

Initially at step 802, when the clinician operates the approximationknob 101 of the circular stapler, a controller of the circular staplermonitors the force from a force sensor 300 disposed in the handleassembly 100 disposed on the proximal end of the outer tube 206. Theforce sensor 300 includes a force sensitive resistor and/or a straingauge. It is contemplated that an optional second force sensor (e.g., aproximal force sensor 300 FIG. 6 ) may be used to additionally monitorstapling force at a second location in the surgical device 1, thusallowing for additional accuracy. In aspects, the force sensor 300 maybe located at the proximal portion of handle assembly (FIG. 3 ) or thedistal portion of the handle assembly (FIG. 6 ) of the stapling device1.

Next, at step 804, the controller 147 provides an indication of thesensed force. For example, the indication of the force may includevisual feedback (e.g., LEDs or a display) based on the sensed force,audible feedback (e.g., a beep, or a voice), and/or additional hapticfeedback (e.g., by a motor vibrating the handle to indicate the sensedforce) based on the sensed force. For example, the surgical device 1 mayinclude three separate color LEDs and/or a multicolor LED.

Next, at step 806, the controller 147 may determine if the sensed forceis within a force range, for example about 100 to about 150 lbs. Theforce range may include a range from a set of predetermined rangesbetween 0 and about 250 lbs. (e.g., 0-50, 50-100, 100-150, etc.). Thecontroller 147 may blink the LEDs, where LED colors indicate a forcewithin a predetermined range. In aspects, the compared force may be usedto determine if the force is within the predetermined force range. Theindication of the sensed force will guide the clinician to the middle ofthe force range.

Next, at step 808, the controller 147 may provide an indication that theforce is within the force range. For example, the user may see a seriesof lights as indicators of force being applied during clamp. This systemsuggests that unwanted levels of tissue compression are not occurringduring the clamping phase of the surgical device 1. When this force isreduced there can be higher confidence that integrity of the tissuevasculature and structure has not been compromised. The combined forcesensitive and feedback system can improve circular stapling operationsduring EEA.

In aspects, controller 147 may output a visual warning message to theuser to slow down clamping speed and allow tissue to relax beforeproceeding. For example, the controller 147 may light the center LED 706green.

After the stapling sequence is completed, the user presses the firebutton 20 to commence the stapling sequence, cut the stapled andcompressed tissue, and form the anastomosis.

Next, at step 810, the controller 147 may determine that the sensedforce is out of the safe range and disable firing.

During the stapling procedure, users rotate the approximation knob 101until a gauge on the surgical device indicates that the gap between theanvil assembly 500 and cartridge is in a safe region to fire and that aninternal range switch (not shown) is activated. In addition to tactilefeedback, the visual feedback provided by the visual indicators 202allow for surgeons to understand the magnitude of the force they areapplying to the tissue. Thus, a user can ensure that there is enoughtime for interstitial fluids to leave the stapling site, therebyavoiding increased force during clamp. When the clamp speed is reduced,so is the force imparted by the anvil assembly 500. The force sensor 300and visual feedback will ensure that users are aware of the force theyare applying during clamp and enable safe stapling practice in terms ofmanual clamping across all surgeons. Less stress on the stapled tissueand vasculature is important for there to be greater perfusion to thestaple line post anastomosis. Greater perfusion can lead to improvedhealing.

In aspects, the controller 147 may provide an indication that it is safeto fire the surgical device. In aspects, a subsequent switch (not shown)may be used to ensure the device has been clamped to an appropriate gap.A force too low can indicate the device should not be fired as itindicates no anvil attached.

Since the controller 147 monitors the force sensor 300 in real time, itis contemplated that the controller 147 may continuously adjust themotor 152 output to achieve a target stroke.

In aspects, the controller 147 may calculate a difference between afirst measurement of the distal force sensor 300 and a secondmeasurement of the proximal force sensor 301. The controller 147 mayperform a comparison of the first and second force to improve theaccuracy of the force measurement. In aspects, if the measured force isabove the maximum stapling force, which may be about 250 lbs., thecontroller 147 disables firing and displays a sequence on the display146 instructing the user the steps to exit the stapling sequence.

In aspects, the distal portion 400 (FIG. 1 ) may use a replaceablereload which includes a storage device 402 configured to store operatingparameters of the reload 400 including starting clamping force, maximumclamping force, a force factor, and the like. Each type of reload 400may have a corresponding starting clamping force, which the controller147 may obtain automatically by reading the starting clamping forcevalue from the storage device 402 and/or set manually by the user byselecting either the type of the reload or the clamping force directly.Starting clamping force may be any suitable threshold from about 100pounds to about 200 pounds, in embodiments, the target clamping forcemay be approximately 150 pounds. For example, a 33 mm sized reload 400may have a clamping force of about 150 lbs.

Although circular stapling devices have been used as examples, thedisclosed technology may be used with linear stapling instruments.

It will be understood that various modifications may be made to theembodiments of the presently disclosed adapter assemblies. Therefore,the above description should not be construed as limiting, but merely asexemplifications of embodiments. Those skilled in the art will envisionother modifications within the scope and spirit of the presentdisclosure.

In one or more examples, the described techniques may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored as one or more instructions orcode on a computer-readable medium and executed by a hardware-basedprocessing unit. Computer-readable media may include non-transitorycomputer-readable media, which corresponds to a tangible medium such asdata storage media (e.g., RAM, ROM, EEPROM, flash memory, or any othermedium that can be used to store desired program code in the form ofinstructions or data structures and that can be accessed by a computer).

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor” as used herein may refer toany of the foregoing structure or any other physical structure suitablefor implementation of the described techniques. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

What is claimed is:
 1. A surgical device comprising: a tool assemblyincluding: a distal portion including a plurality of staples; and ananvil assembly being movable relative to the distal portion from an openposition to a clamped position; a handle assembly including: anapproximation mechanism coupled to the anvil assembly and configured tomove the anvil assembly from the open position to the clamped position;a force sensor disposed at a distal end of the surgical device, theforce sensor configured to sense a change in electrical resistanceindicating a compression force on tissue, wherein the force sensorincludes: a substantially circular substrate including a proximal sideand a distal side; a conductive trace disposed on the distal side of thesubstrate; and a conductive material disposed on the conductive trace;and a controller configured to: receive a signal indicative of a forcemeasured by the force sensor; and provide an indication of the sensedforce.
 2. The surgical device according to claim 1, wherein theindication of the force includes at least one of visual feedback, hapticfeedback, or audible feedback based on the measured force.
 3. Thesurgical device according to claim 1, wherein the distal force sensorincludes a force sensitive resistor.
 4. The surgical device according toclaim 1, wherein the trace includes an interdigitated pattern.
 5. Thesurgical device according to claim 1, wherein the conductive materialincludes a conductive sheet or a conductive ink.
 6. The surgical deviceaccording to claim 1, wherein the conductive material includesconductive and non-conductive particles suspended in a matrix.
 7. Thesurgical device according to claim 1, wherein the controller is furtherconfigured to: transmit the indication of the sensed force to a display.8. The surgical device according to claim 1, wherein the controller isfurther configured to: determine if the sensed force is within a forcerange; and provide an indication that compression forces on the tissueare within a predetermined range.
 9. The surgical device according toclaim 1, wherein the distal portion and the anvil assembly are circular.10. A method for providing an indication of force for a surgical device,the method comprising: sensing a force measured by a distal force sensordisposed at a distal end of a surgical device, the distal force sensorconfigured to sense a change in resistance indicating a force impartedon an approximation mechanism of the surgical device, wherein the distalforce sensor includes: a substantially circular substrate including aproximal side and a distal side; a conductive trace disposed on thedistal side of the substrate; and a conductive material disposed on theconductive trace; and providing an indication of the sensed force duringclamping tissue.
 11. The method according to claim 10, furthercomprising transmitting the indication of the sensed force to a display.12. The method according to claim 10, further comprising: determining ifthe sensed force is within a force range; and providing an indicationthat compression forces on the tissue are within a predetermined range.13. The method according to claim 10, wherein the indication of theforce includes at least one of visual feedback based on the sensedforce, haptic feedback, or audible feedback based on the sensed force.14. The method according to claim 10, wherein the force sensor includesa force sensitive resistor.
 15. A force sensor configured to sense achange in resistance indicating a force imparted on an approximationmechanism, the force sensor comprising: a substantially circularsubstrate including a proximal side and a distal side; a conductivetrace disposed on the distal side of the substrate; and a conductivematerial disposed on the conductive trace.
 16. The force sensoraccording to claim 15, wherein the trace includes an interdigitatedpattern.
 17. The force sensor according to claim 15, wherein theconductive material includes a conductive sheet or a conductive ink. 18.The force sensor according to claim 15, wherein the conductive materialincludes conductive and non-conductive particles suspended in a matrix.19. The force sensor according to claim 15, wherein the conductivematerial includes a distal side and a proximal side, and wherein theforce sensor further includes an actuator disk disposed on the distalside of the conductive material.